U2 vs. U3 and some semi-scientific rambling
Hi!
There are multiple threads where the U3 is discussed in comparison to the U2 – and I found them very interesting. Also, having had some technical training regarding visual perception, color and the way we really see, I would pay particular attention to the points made by the more knowledgeable among us regarding the difference between the numbers (specs) and what the human eye can actually perceive.
It turns out that it takes a significant (percentage) increase in the number of lumens for the eye to discern a difference in brightness. Not only that, perceived brightness is highly dependent on the spectral distribution of the light and even the individual observer.
I would love to see someone address this subject in much more detail because it definitely relates to our hobby and it turns out to be a fascinating one.
I’m about to depart from the subject a little but please allow me to relate part of an experiment done by Edwin Land (founder of Polaroid and a serial inventor). I believe the experiment was done in the 60s after Land invented the polarizing filter. (My guess is that you will not believe what I’m about to describe – but I replicated a form of the experiment as part of a junior high school science project.) Please read on because it’s quite fascinating:
1) Take two slide projectors with black and white (not color) slides, both taken of the same scene.
2) Then, superimpose the images on an ordinary screen but in a dark room.
3) Take a narrowband red filter and attach it to the front of one of the projector lenses.
3) Now, look at the superimposed images on the screen.
4) The Big Question – what do you see?
5) The amazing answer – you see/perceive a scene with a full spectrum of colors!
Why???? Well, I have a T-Shirt that says “I can explain it to you but I can’t understand it for you.” To be frank, I still don’t totally understand this phenomenon but there is a great write-up of the experiment in addition to a couple others along the same lines in an old Scientific American magazine.
By the way, Land did pursue the phenomenon as a potential method for producing his first marketable instant color film.
I asked him (through his assistant) why he didn’t end up commercializing the results and part of the answer had to do with his inability to get adequate color saturation.
ADDENDUM #1) There is a little more to this than I’m describing but one key point is that the two slides were taken under different circumstances. Yes, they were both taken with black and white film but one was taken with a red filter on the lens and the other was not. Other scientists, layman and photographers would say that comes nowhere near explaining how two black and white slides and one red filter can produce a spectrum of color. Before seeing it for themselves everyone you query will predict that you will produce an image that ranges in color from red to black with various shades of pink in-between.
The traditional view of how the eye perceives light and color were challenged by the results of this and related experiments and to this day, the whole “rod and cone” explanation and all that goes along with it survives pretty much intact regardless.
ADDENDUM #2) I could go on for pages about this topic but this is neither the time nor the place for that type of dissertation.
Back to a subject relevant to the BLF and flashlights:
I have taken a keen interest in High CRI LEDs – not what Cree calls High CRI, but something well into the 90 plus percent range. In reading comments and discussing this subject with quite a few members, I’ve found that it’s a subject that most people have trouble “getting their head around.”
The difference between a CW XML and an NW XML is in the difference between the AVERAGE spectral temperatures of the light they produce – as measured in Kelvin. It turns out that neither LED, whatever Kelvin you decide is NW, will actually reflect back the full range of real life colors proportionate to the way they appear under “natural light.” In fact, the difference is huge. Let me suggest we set aside what we want to call “natural light” for the moment and concentrate on what those LEDs are doing to what we actually see when we shine one of our flashlights on a colorful scene at night.
This subject has also been covered in other threads and I don’t want to go on forever but what is clear is that there is a lot misconception and misunderstanding.
Allow me to be intentionally provocative for a moment – the purpose being to stimulate interesting debate and encourage others to “pick these points up where I leave off.”
A) The beam comparisons that we see in tests are interesting, fun, and instructive but often highly misleading – and what appears to be a significant difference in output intensity (accurately measured in lumens) is totally unimportant. Take one of the lights out to walk your dog tonight and take the other out tomorrow night. All else being equal, you won’t notice a difference even though there is a rather large difference in lumens.
B) The binning and labeling process that Cree uses leave a lot to chance. An LED that is rated as having a higher output may indeed have a lower output as measured by accurate instruments – that’s partly because the process is simply not that accurate (something that Cree admits in their specs – and it may be even less accurate than they say- or than sellers would have you believe). Add that fact to the logarithmic nature of the eye’s sensitivity to light and these numbers that we throw around with so much import, should be taken far more lightly (pardon the pun).
C) IMHO, almost all of us (and I include myself here), make buying decisions based on the wrong criteria!
D) COLOR ACCURACY gets short shrift: Personally, I think it would be great if we could see comparison shots of an array of color construction paper or a colorful real-life scene. I’m not sure how this would be accomplished but if we’re comparing two flashlights, rather than having two photos, how about three – one being taken in “natural light” so that we know what those colors should actually look like.
Granted, its fun to see how far away something can be while still being able to light it up. To cite another example, if you’re riding your bike at night, it’s certainly not as important to see the “natural color” of that pothole in the road as it is to see it in time to avoid it in time.
Needless to say, there are many examples like the above but I would say that color accuracy has gotten “short shrift” in our discussions and tests – just an opinion (and debate is welcome).
E) “Pencil Beam” vs. “Peripheral Vision”: I often finding myself trying to find something in a dark area. A flooder, a zoomer or even a light with a really good usable spill are essential to my practical use of a light. There are those that use their lights strapped to a hunting rifle or some other specialized purpose but how many of us pick up a light simply to impress our friends with how far off it will shine? Please don’t think I frown on this practice. It’s fun! – And I do it myself. On the other hand, if a light is going to get good use and not be relegated to “shelf-queen” status, how should it function? Again – opinions and debate welcome.
F) Quality, Durability and User Interface: I throw these topics in together solely for lack of time and space. Collectively, these areas are almost always attended to by our fantastic reviewers. I just wish all the manufacturers did the same. I could never be part of the “money is no object crowd” but I do find myself paying more and more attention to these things and my sense is a lot of us our doing ourselves a disservice by ignoring them – more on these topics later
Epilogue: Sorry to bore you with a lot of rambling – just had some time to burn and felt “semi-philosophical” for moment. Take it for what it’s worth.
Regards and HAPPY NEW YEAR!
KumaBear Bob
